Nearly all the colleges at oxford are within 30mins walk of the medical faculty, so don't worry about that, I would choose one you liked the look of because it doesn't really matter too much and everyone ends up loving their college.
I think you should apply to the one you liked more, you have relatively similar UMS and GCSEs in terms of how they would look at them so I would focus on acing the BMAT, but I think you would almost definitely get an interview at cambridge, they interview nearly everyone, but oxford throws lots of people out after the BMAT before interview.
Also I think they calculate the UMS differently if you do further maths too, but I don't know the specifics.
Good luck, sorry I can't be more helpful.